Piston engines, and in particular internal combustion engines, are often cooled using lubrication oil. This is conventionally achieved by spraying lubrication oil onto the piston to facilitate heat transfer between the piston head and the sprayed lubricant. The heated oil then flows down to a sump from where it is recycled by a pressurized lubrication system. In a dry-sump lubrication system, the sump flow is first scavenged to a storage tank which is usually located remotely from the sump itself.
Such heat transfer, however, is inefficient, as the contact time between the piston and the oil spray is short. Moreover, the small contact area at the rear face of the piston also hampers efficient heat transfer. Due to these inefficiencies, a relatively large volume of oil spray having a high flow rate is required to cool the piston. This large volume of oil having a high flow rate requires additional components such as larger-than-necessary oil storage tanks, thereby reducing the engine's power-to-weight ratio and increasing the manufacturing and operational costs of the engine.
Some systems, however, teach a closed-loop oil system in which lubrication oil flows through the crankshaft, the connecting rod, and the piston. There are a number of drawbacks associated with such systems. First, lubrication oil does not make sufficient contact with the piston for a sufficient length of time to efficiently remove heat from the piston. Second, flow channels within different pistons are typically serially connected such that lubrication oil heated by a preceding piston is used for cooling a subsequent piston. Therefore, the lubrication oil cooling different pistons has different temperatures. Accordingly, heat transfer between a piston and the lubrication oil is not uniform across the engine. This causes thermal gradients and strains within the engine potentially leading to the formation of cracks, etc.
In light of the above, it would be highly desirable to provide an efficient cooling system for a piston engine while maintaining a high power-to-weight ratio and reducing costs.